Matrix protein of rabies virus is responsible for the assembly and buddingof bullet-shaped particles and interacts with the transmembrane spike glycoprotein G

To elucidate the functions of rhabdovirus matrix (M) protein, we determined the localization of M in rabies virus (RV) and analyzed the properties of an M-deficient RV mutant. We provide evidence that M completely covers the ribonucleoprotein (RNP) coil and keeps it in a condensed form. As determine d by cosedimentation experiments, not only the M-RNP complex but also M alo ne was found to interact specifically with the glycoprotein G, In contrast, an interaction of G with the nucleoprotein N or M-less RNP was not observe d. In the absence of hi, infectious particles were mainly cell associated a nd the yield of cell-free infectious virus was reduced by as much as 500,00 0-fold, demonstrating the crucial role of M in virus budding. Supernatants from cells infected with the M-deficient RV did not contain the typical bul let-shaped rhabdovirus particles but instead contained long, rod-shaped vir ions, demonstrating severe impairment of the virus formation process. Compl ementation with M protein expressed from plasmids rescued rhabdovirus forma tion. These results demonstrate the pivotal role of M protein in condensing and targeting the RNP to the plasma membrane as well as in incorporation o f G protein into budding virions.